Purification and characterization of the enzymes of fructan biosynthesis in tubers of Helianthus tuberosus 'Colombia': I. Fructan : fructan fructosyl transferase

Fructan : fructan fructosyl transferase (FFT), one of the enzymes involved in the synthesis of β-2,1 linked fructose polymers has been purified 205-fold from tubers of Helianthus tuberosus harvested in the accumulation phase. The molecular weight of the native as well as the SDS-denatured protein is approximately 70 kDa. On IEF, the protein was separated into five molecular species with p/ values between pH 4.5—5.0. The optimum pH for fructosyl transfer activity was between 5.5—7.0. Temperature optimum was in the range of 25—35 °C; the Q10 value between 25 and 5 °C was 1.14. FTT catalysed the self-transfer of fructosyl groups with GF2, GF3, GF4 or GF5 as substrate and acceptor. The rate of self-transfer with both GF2 and GF3 increased linearly with substrate concentration up to 100 mol m-3 and was still not saturated at 600 and 300 mol m-3, respectively. FFT was unable to hydrolyse GF or to catalyse the self-transfer with GF but could mediate the transfer of fructosyl units from inulin on to GF.